Medical problems that affect bones, including fractures, degenerative diseases and inflammatory syndromes, impact millions of people worldwide. Bone fractures, lower back pain, osteoporosis, scoliosis and other musculoskeletal problems generally require orthopedic intervention with the use of permanent or temporary medical surgical fixation devices. The properties of these fixation devices play a key role in determining the success and recovery time for the medical procedures.
Surgical fixation devices, including plates, screws, pins, rods, anchors and staples, are used in orthopedic surgery procedures, such as: bone fracture fixation (Weiler et al., 1988, Am. J. Sports Med. 26(1):119-28); autograft ankle stabilization (Jeys et al., 2004, Am. J. Sports Med. 32(7):1651-59); reconstruction surgery of the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) (Nakano et al., 2000, Clin. Biomech. 5(3):188-95); replacement of the intervertebral discs (Ella et al., 2005, J. Mat. Sci.-Mat. Med. 16(7):655-62); and posterior spinal fixation (Evans et al., 2002, J. Mat. Sci.-Mat. Med. 13(12):1143-45).
Metal surgical fixation devices are often used to replace damaged or missing bone tissue due to their high initial fixation strength (Kurosaka et al., 1987, Am. J. Sports Med. 15(3):225-29; Lambert, 1983, Clin. Orthop. Rel. Res. 172:85-89; Shelbourne & Nitz, 1990, Am. J. Sports Med. 18(3):292-99). However, metallic implant devices are not degradable, leaving cavitations in the bone once the devices are removed.
In recent years, surgical fixation devices prepared with biocompatible polymers have been investigated as potential replacements of metallic fixation devices. Biocompatible polymers have the potential to revolutionize biomedical engineering as scaffolds for hard and soft tissues, such as bone and blood vessels. Compared with conventional metal fixation devices, biocompatible polymer-based fixation devices have the advantages of causing no long-term implant palpability, no long-term temperature sensitivity, no stress shielding and no interference with post-operative diagnostic imaging. These advantages may lead to better bone healing, reduced patient trauma, reduced cost, elimination of need for a subsequent surgery for implant removal, and fewer complications from infections.
However, biocompatible polymer-based fixation devices still face challenges. The polymer or composite used in the devices should have good biocompatibility with the surrounding tissue and have mechanical properties similar to the bone tissue being replaced. Furthermore, the polymer or composite should be biodegradable so that it is gradually replaced by newly grown tissue (Claes et al., 1986, Akt. Traumatol. 16:74-77; Rokkanen et al., 1985, Lancet 1(8443):1422-24). Most current biocompatible polymers are not strong enough from a mechanical standpoint, especially when used as surgical fixation devices and bone scaffolds. Furthermore, current biocompatible polymer-based surgical fixation devices do not actively promote bone healing and regrowth, leaving voids in the tissue once the implanted device is fully degraded. There is thus a need to identify a polymer or composite material that combines structural strength and bone tissue regrowth stimulation.
Nanosized diamond powders (also known as nanodiamonds or NDs) are produced by detonation synthesis in large volumes (Shenderova & McGuire, “Nanocrystalline Diamond,” in “Nanomaterials handbook,” Y. Gogotsi, Ed., 2006, CRC Taylor and Francis: Boca Raton, p. 203-37) and represent a new class of relatively inexpensive carbon nanomaterial with a broad range of potential applications, including composite materials. NDs have been used as components of sorbents, lubricating and polishing compositions and as additives to electrolytic and electroless deposition baths.
NDs are composed of particles of about 5 nm in diameter and consist of an inert diamond core terminated with surface chemical groups such as C═O, COOH, and OH (Lam et al., 2008, ACS Nano 2(10):2095-2102), as shown in FIG. 1. When originally synthesized, the diamond core is often surrounded by graphene shells and amorphous carbon (FIGS. 1a and 1b; Osswald et al., 2006, J. Am. Chem. Soc. 128(35):11635-42).
NDs are a member of the nanocarbon family, but differ from other well-known nanomaterials, such as fullerenes and carbon nanotubes (Shenderova et al., 2002, Crit. Rev. Solid State Mat. Sci. 27(3-4):227-356). NDs exhibit the excellent mechanical, thermal and electrical properties of diamond at nanoscale, and actually outperform carbon nanotubes (CNTs) and other known materials. For example, the thermal conductivity of nanodiamonds (˜2000 W·m−1·K−1) is of the same order as the highest reported for CNTs (6600 W·m−1·K−1) (Berber et al., Phys. Rev. Lett. 84(20):4613-16). However, in contrast to carbon nanotubes, ND is a good insulator.
An attractive characteristic of NDs is their relative lack of toxicity and their biocompatibility. NDs have recently been reported to be the least toxic of all carbon nanomaterials (Puzyr et al., 2007, Diamond Relat. Mater. 16:2124-28; Huang et al., 2007, Nano. Lett. 7(11):3305-14; Mitura et al., 2006, J. Achiev. Mat. Manuf. Eng. 16(1-2):9-16; Bakowicz-Mitura, 2007, Surf. Coat, Technol. 201(13):6131-35; Lam et al., 2008, ACS Nano 2(10):2095-2102; Liu et al., 2007, Nanotechnol. 18(5):55102; Schrand et al., 2007, J. Phys. Chem. B 111(1):2-7; Puzyr et al., 2007, Diamond Relat. Mater. 16:2124-28). In contrast, the toxicity of CNTs is still debatable and raises concerns regarding their use in biological applications (Cherukuri et al., 2004, J. Am. Chem. Soc. 126(48):15638-39; Cherukuri et al., 2006, Proc. Natl. Acad. Sci. U.S.A. 103:18882-86).
The small particle size and the low toxicity of NDs make them desirable for biological applications. Still, many potential applications of NDs, including in biomedical and composite materials, remain unexplored.
There remains a need in the art to identify novel materials that are compatible with biological systems and may have used in biomedical applications, such as orthopedic surgery. The present invention fulfills these needs.